“We clearly heard the first shot and probably 20 more shots,” Zach said.

Zack said his teacher ran into the hallway and pulled the fire alarm to alert everyone on the other side of the building. That quick-thinking teacher may have saved lives.

The students in Zack's classroom barricaded the door and took cover.

Photos: At least 8 killed in shooting at Santa Fe High School

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His girlfriend, Lauren Little, was in math class on the opposite side of the school when they heard the fire alarm. Her teacher said there wasn't a drill scheduled and she immediately began ushering them out of the building.